In an article appearing in the October, 1967, volume of the "Air Conditioning, Heating and Ventilation" magazine, Milton Eaton, the inventor of the present invention, suggested that an electrode steam boiler of the type known as an Eaton automatic electric steam generator and described in Section 8 - 13, Standard Handbook for Electrical Engineers be used as the direct source of HTW for a heating system.
In the system shown and described in that article, steam was to be removed from the boiler for steam heating purposes and an additional limited amount of steam was to be removed for control purposes. HTW was to be taken from the boiler for supply to a HTW heating circuit. A proportioning valve was interconnected between the boiler and HTW heating system.
Mr. Eaton has subsequently found it is necessary to provide for unrestricted flow of HTW from the boiler to the heated spaces circuit in order for the boiler to serve as a pressurized expansion tank for the heating system. This is because action of the proportioning valve would, from time to time, restrict flow of HTW from the boiler to the HTW heating system. This would cause loss of pressure in the heating system with consequent occurrence of flash steam that would prevent normal circulation of HTW through the system.
Mr. Eaton has further discovered that an electrode steam boiler of the type known as an Eaton automatic electric steam generator will operate normally as a source of HTW with the steam output limited to that required for automatic control purposes. The boiler water is circulated as HTW through a space heating system and returned to the boiler where it is heated to steam temperature as required for the boiler steam pressure controller to maintain the boiler steam pressure at the controller set point. It is not necessary to remove the relatively large amounts of steam associated with a steam heating system, for instance. However, the boiler may be used as the source of steam for other services not associated with the HTW space heating system.
Design features of the Eaton automatic steam boiler that make it suitable for this application are (1) the boiler load can be limited to the steam output required for control purposes, (2) the water-jet action whereby water is taken from the boiler, water from an outside source mixed with it, and the mixture is pumped through water spouts with nozzles and directed towards the tips of the electrodes with sufficient velocity to flow up the sides of the electrodes to the water level controlled by the boiler steam pressure controller, and (3) the tip-shielded electrode.
For use in supplying HTW for a space heating system, however, provision must be made to prevent adverse operating conditions and to provide suitable conditions for normal operation.